You could often get twice the performance on the PC side 6months down the road for 1/4 the price as a Mac Pro, which I don't think are no longer made.

The Mac Pro is a Xeon workstation. Dell doesn't give those away for free, either.

A quick trip to the Apple site would show you that the Mac Pro is still available in the U.S. (Apple has reportedly stopped selling the Mac Pro in EU countries due to new EU regulations on shielding fans and electrical ports, which the existing design would apparently fail).

An issue with the Mac Pro is that there has been no major update in some time (e.g., still no Thunderbolt or USB 3.0 ports). Apple has talked about something coming in 2013 but has not given any details.